1. Technical Field
The present invention relates to metering valves, and in particular, to hydraulically driven valves suitable for use in high pressure environments, such as in the ignition and sustained combustion systems of air and space vehicles.
2. Description of the Related Art
Valves for metering fuel and other combustible media to engines in aircraft and spacecraft are known in the art, see e.g., U.S. Pat. No. 6,250,602 B1, assigned to the assignee of the present invention. Such valves are used to control the rate at which pressurized fuel, in a liquid or gaseous state, is supplied to the ignition injectors or the inlet orifices in the engine combustion chambers. The valves are relied upon to provide consistent and rapid control of flow rates of fuel at ignition and during sustained operation. Their operation is critical to proper performance of the vehicle. Poor valve operation can result in unintended engine shutdown and failure.
These valves can have movable stem-like valve members, or pintles, aligned with the outlet port of the valve for controlling the rate at which fuel flows to the engine. Pintle type valves are typically less affected by the temperatures and pressures of the fuel passing through the fuel chamber of the valve, due to their contoured head and axial movement. However, even pintle valves can be adversely affected by the high pressure and temperature conditions of jet engines.
Jet engines often ignite by burning an ignition medium, such as Ethylene, in a gaseous state at elevated pressures and temperatures. The extreme environment can cause significant loading on the metering components that can effect movement and sealing, and can lead to improper performance or failure of the valve.
Hydraulic valves have been used for such applications in which a pressurized fluid is used to drive an actuator in turn driving the metering components. To minimize weight in air and space vehicles, the hydraulic fluid driving the valve can be the pre-burned fuel in a liquid state. Such valves are known in the industry as “fueldraulic” valves.
Conventional fueldraulic valves typically do not provide adequate cooling for use with supersonic combustion ramjet (“scramjet”) engines, which fly between Mach 4 and Mach 10 in the earth's atmosphere. However, U.S. Pat. No. 6,783,108 B2, assigned to the assignee of the present invention, discloses a fueldraulic valve that is designed to operate accurately and reliably in the high pressure and temperature conditions of delivery fuel to scramjet engines for sustained combustion. The disclosed valve managed heat dissipation using a unique baffle that better directed the fuel in proximity to the actuation, sealing and other components of the valve. However, the disclosed valve was designed for use in a sustained combustion fuel delivery system with a less extreme pressure environment of approximately 700 psia.
For the ignition system of a scramjet engine, on the other head, a very high pressure supply of ignition media, such as Ethylene at 4,000 psia, may be used, largely to reduce the size and weight of the tank. In order for conventional valves to accurately and reliably meter ignition media at such high pressures, a separate pressure regulator was used to step down the pressure. This two-stage approach is disadvantageous because the additional component both adds to the space and weight requirements of the system and introduces another point for breakdown, leakage and failure in the critical flow path of ignition media.